a b s t r a c tAdolescents' school-based friendship networks tend to be segregated along ethnic lines. But few studies have examined whether variation in network boundaries affects the degree of ethnic friendship segregation. We use rational-choice theory to argue that ethnic homophily is more pronounced for friendships between classrooms than for those within classrooms. We empirically test this hypothesis using twowave German panel data (N = 1258) and stochastic actor-oriented models (RSiena). In line with our theoretical argument, we find that the tendency to form same-ethnic friendships is indeed stronger at the grade level, which translates into stronger ethnic segregation in friendship networks at the grade level than at the classroom level. Implications for research on ethnic segregation in school-based friendship networks are discussed.

Individual preferences for same-ethnic friends contribute to persistent segregation of adolescents’ friendship networks. Yet, we know surprisingly little about the mechanisms behind ethnic homophily. Prior research suggests that ethnic homophily is ubiquitous, but a social identity perspective indicates that strong ingroup identification drives ingroup favoritism. Combining a social identity perspective with a relational approach, we ask whether the presumed increased homophily of high identifiers extends to all ingroup members, or whether it is conditional on the strength of same-ethnics’ identification. We propose that the strength of ethnic identification affects not only how much individuals desire same-ethnic friends, but also how attractive they are as potential friends to others. Fitting stochastic actor-oriented models to German adolescent school-based network panel data, we find that ethnic homophily is driven by an interplay of peers’ ethnic identification: high identifiers befriend same-ethnic peers who share their strong ethnic identification, while excluding same-ethnic low identifiers. Low identifiers, in turn, tend to avoid befriending inter-ethnic high identifiers. Our relational approach reveals that ethnic homophily is hardly ubiquitous but requires strong identification of both parties of a (potential) friendship.

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